Application off Sharpless asymmetric epoxidation on the preparation of the optically active flavours 3-methylthiohexanal and 5(6)-butyl-1,4-dioxan-2-one

摘要

Optically active 2,3-epoxyhexanol obtained from Sharpless asymmetric epoxidation (AE) was regioselectively reduced to 1,3 hexandiol or 1,2-hexandiol. 1,3-Hexandiol was converted to 3-mesyloxyhexyl acetate. The following reaction with CH3SK gave 3-methylthiohexanol, which was oxidized through Swern oxidation to produce 3-methylthiohexanal. 5- and 6-Butyl-1,4-dioxan-2-one were formed concurrently by the reaction of 1,2-hexandiol with 2-bromoacetic chloride and the ratio of 5-butyl isomer to 6-butyl isomer was about 1:4. The enantiomeric excess values of both enantiomers of 3-methylthiohexanal and 5(6)-butyl-1,4-dioxan-2-one were about 90%, which were very close to those of 2,3-epoxyhexanol (about 94% ee). No obvious racemization occurred during the transformation from the Sharpless AE products to the final products.